## Summary

This following is a behavior from CRuby 1.8.7 to 3.1.0.

```console
% ruby -ve "p ['a', 'b', 'c']*''"
ruby 1.8.7 (2013-12-22 patchlevel 375) [i686-darwin13.0.2]
"abc"

% ruby -ve "p ['a', 'b', 'c']*''"
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin19]
"abc"
```

### Before (mruby 3.0.0)

mruby unexpectedly gives the TypeError.

```ruby
['a', 'b', 'c']*'' #=> String cannot be converted to Integer (TypeError)
```

### After

This PR makes mruby behave compatible with CRuby.

```ruby
['a', 'b', 'c']*'' #=> 'abc'
```

As far as I checked, the behavior is unspecified when `Array#*`'s argument
is not an instance of Integer class in X 3017 : 2013 (ISO/IEC 30170 : 2012).

## Additional Information

I noticed this difference by the following idiom when writing ASCII art code
using Ruby.

```ruby
%w(foo bar baz)*''
```

e.g. TRICK (https://github.com/tric)